The present invention relates to an engine exhaust purification device provided with a catalyst.
JP-A-H9-228873 published by the Japanese Patent Office in 1997 discloses a technique wherein an oxygen amount stored in a three-way catalyst (hereafter, xe2x80x9coxygen storage amountxe2x80x9d) is estimated based on an engine intake air amount and an air fuel ratio of an exhaust flowing into the catalyst, and engine air-fuel ratio control is performed so that the oxygen storage amount of the catalyst remains constant.
To maintain the NOx (nitrogen oxides), CO and HC (hydrocarbon) conversion efficiency of the three-way catalyst at a maximum, the catalyst atmosphere must be maintained at the stoichiometric air-fuel ratio. If the oxygen storage amount of the catalyst is maintained constant, oxygen in the exhaust is stored in the catalyst even if the air-fuel ratio of the exhaust flowing into the catalyst temporarily becomes lean. Conversely, oxygen stored in the catalyst is released even if the air-fuel ratio of the exhaust flowing into the catalyst temporarily becomes rich, so the catalyst atmosphere can be maintained at the stoichiometric air-fuel ratio.
In an exhaust purification device which performs this control, the conversion efficiency of the catalyst depends on the oxygen storage amount of the catalyst. Therefore, the oxygen storage amount must be precisely computed to control the oxygen storage amount to be constant and maintain the conversion efficiency of the catalyst at a high level.
It would be an advantage to precisely compute an oxygen storage amount in an exhaust purification device for controlling the air fuel ratio of an engine provided with a three-way catalyst so as to maintain the oxygen amount constant, and to maintain the conversion efficiency of the catalyst at a high level.
According to one embodiment there is provided an exhaust purification device for an engine, the device comprising a catalyst provided in an exhaust passage of the engine, a front sensor which detects an oxygen concentration in the exhaust gas flowing into the catalyst, and a microprocessor programmed to compute an oxygen storage amount of the catalyst separately for a high speed component which has a rapid oxygen storage rate and a low speed component which has a slower storage rate than that of the high speed component based on the oxygen concentration of the exhaust gas, assuming that when oxygen is released, the oxygen is released preferentially from the high speed component rather than from the low speed component when the ratio of the low speed component to the high speed component is less than a predetermined value, and control the air-fuel ratio of the engine based on the computed oxygen storage amount so that the oxygen storage amount of the catalyst is a predetermined amount.
According to another embodiment, there is provided a method of estimating an oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to change at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; and wherein the first rate is estimated based on a relationship between the first amount and the second amount.
According to yet another embodiment, there is provided a method of estimating an oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to be stored at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; and wherein the first rate is estimated based on a relationship between the first amount and the second amount.
According to yet another embodiment, there is provided a method of estimating an oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to be released at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; and wherein the first rate is estimated based on a relationship between the first amount and the second amount.
According to yet another embodiment, there is provided a method of controlling the oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to change at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; wherein the first rate is estimated based on a relationship between the first amount and the second amount; and controlling an air/fuel ratio of the engine based on the estimated first amount.
According to yet another embodiment, there is provided a method of controlling the oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to be stored at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; and wherein the first rate is estimated based on a relationship between the first amount and the second amount; and controlling an air/fuel ratio of the engine based on the estimated first amount.
According to yet another embodiment, there is provided a method of controlling the oxygen storage amount of a catalyst within a catalytic converter coupled to an engine. The method comprises estimating a first amount of oxygen stored in the catalyst, the first amount representing a part of the oxygen storage amount, the first amount estimated to be released at a first rate; estimating a second amount of oxygen stored in the catalyst, the second amount representing another part of the oxygen storage amount; wherein the first rate is estimated based on a relationship between the first amount and the second amount; and controlling an air/fuel ratio of the engine based on the estimated first amount.
According to yet another embodiment, there is provided an exhaust purification device for an engine. The device comprises a catalyst provided in an exhaust passage of the engine; a front sensor which detects an oxygen concentration of oxygen flowing into the catalyst; and a microprocessor programmed to: estimate a first amount of oxygen stored in the catalyst, the first amount estimated to change at a first rate; estimate a second amount of oxygen stored in the catalyst; wherein the first rate is estimated based on the oxygen concentration and a relationship between the first amount and the second amount; and control an air/fuel ratio of the engine based on the estimated first amount.
According to yet another embodiment, there is provided an exhaust purification device for an engine. The device comprises a catalyst provided in an exhaust passage of the engine; a front sensor which detects an excess oxygen concentration of oxygen flowing into the catalyst; and a microprocessor programmed to: estimate a first amount of oxygen stored in the catalyst, the first amount estimated to be stored at a first rate; estimate a second amount of oxygen stored in the catalyst; wherein the first rate is estimated based on the excess oxygen concentration and a relationship between the first amount and the second amount; and control an air/fuel ratio of the engine based on the estimated first amount.
According to yet another embodiment, there is provided an exhaust purification device for an engine. The device comprises a catalyst provided in an exhaust passage of the engine; a front sensor which detects a deficient oxygen concentration of oxygen flowing into the catalyst; and a microprocessor programmed to: estimate a first amount of oxygen stored in the catalyst, the first amount estimated to be released at a first rate; estimate a second amount of oxygen stored in the catalyst; wherein the first amount is estimated based on the deficient oxygen concentration and a relationship between the first amount and the second amount; and control an air/fuel ratio of the engine based on the estimated first amount.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.